Vehicle steering control apparatus



March 11, 1952 HAMMOND 2,588,382

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' VEHICLE STEERING CONTROL APPARATUS Original Filed Jan. 18, 1945 11 Sheets-Sheet 9 I Laure/2s fiammand March 11, 1952 HAMMOND 2,588,332

- VEHICLE STEERING CONTROL APPARATUS Original Filed Jan. 18, 1943 ll Sheets-Sheet 1O LEI-'7' r0 EIGHT 721/ enzor Laure/25 Hammond March 11, 1952 HAMMOND VEHICLE STEERING CONTROL APPARATUS Original Filed Jan. 18, 1943 11 Sheeps-Sheet 11 W llllllll l wfiivfiwlk Wx TEQQQQQ 0k ORUMQ Q l l ll f/z VE/Z for Laure/2's 71160102 and Patented Mar. 11, 1952 2,588,382 VEHICLE STEERING C(iNTROL APPARATUS Laurens Hammond, Chicago, Ill., assignor to Hammond Instrument Company, Chicago, 111., a corporation of Delaware 2 Original application January 18, 1943; Serial No. 472,735. Divided and this application July 27, 1944, Serial N0. 546,762

14 Claims.

My invention relates generally to control apparatus and more particularly to improved apparatus for controlling and steering a vehicle, such as a glider, in response to control signals, such for example are provided by radiation from a point to which the vehicle isto be steered.

This application is a division of my copending application, Serial No. 472,735, filed January 18. 1943, which has matured into Patent No. 2,432,151. The amplifying means disclosed herein constitutes the subject matter of an application Serial No. 511,916, filed November 27, 1943, which is also a division of said application, Serial No. 472,735, and which has matured into Patent No. 2,432,151.

In many types of apparatus, particularly those used by the armed forces, it is desirable to be able to detect a source of radiation and to provide means for indicating the direction of the source. In addition, it is frequently desirable to steer a vehicle toward a selected radiation source (whether an original source or a source by reflection) such, for example, as steering a marine torpedo toward a hostile vessel. As disclosed herein, the invention is utilized for automatically steering an explosive carrying glider toward a target in response to light received from the target.

It is thus an object of the invention to provide an improved automatic target seeking apparatus.

A further object is to provide an improved photoelectric detection and amplifying system in which the sensitivity of the amplifying system decreases as the apparatus receives signals of increasing amplitude, for example, as the apparatus approaches a target.

A. further object is to provide an improved radiation detection system in which means are provided for selecting a desired portion of a relatively large radiation source as providing the significant and controlling signal. I

A further object is to provide .an improved scanning apparatus which may be conditioned selectively to scan from right to left (R-L) or to scan from left to right (Ir-R), or to scan both RL and L-R.

A further object is to provide an improved scanning system and apparatus controlled thereby to steer a vehicle toward a selected source of radiation within the field scanned.

A further object is to provide an improved system and apparatus for controlling the flight of a pilotless glider.

Other objects will appear from the following description, reference being had to the accompanying drawings in which:

Figures 1a, 1b, 1c, 1d and 1e together constitute a wiring diagram of the apparatus, the circuits of Fig. 1a forming part of the scanning head, the diagram of Figs. 1b and 1c constituting the amplifier, the diagram of Fig. 1d constituting the which Figs. 1a to 1e are to' be joined to form a complete circuit diagram;

Figure 3 is a plan view, with portions shown in fragmentary section, of the scanning head;

Figure 4 is a side elevational view or the scanning head;

Figure 5 is a front elevational view of the scanning head with portions shown in section;

Figure 6 is a horizontal sectional view taken on the line 6-.6 of Fig. 5;

Figure 7 is a fragmentary sectional view showing the portion of the frictional retarding mechanism;

Figure 8 is a. diagram illustrating the shape and dimensions of the scanned field;

Figure 9 is a fragmentary plan view showing the resilient electrical connectors between the oscillating telescope tubes and the gimbal;

Figure 10 is a diagram showing the wave form of the electrical signal produced when the apparatus scans a single discontinuity;

351 tive wave constituting the input of the limitin electron discharge device;

Figure 13 is a diagram illustrating a representative wave form of the output of the limiting electron discharge device;

Figure 14 is a diagram illustrating the field of view of the apparatus which might be productive of the waves shown in Figs. 12 and 13 in which the target is remote from the apparatus;

Figure 15 is a diagram illustrating the field of view of the apparatus as it approaches more closely to the target;

Figure 16 is a diagram showing the wave form of the output of the upper amplifier when the apparatus is scanning the field represented in Fig. 15;

of the output of the upper amplifier while scanning the field of view illustrated in Fig. 17;

General description In order that the detailed description of the apparatus may be more readily understood, it is preceded by this brief general description of the apparatus as a Whole.

As previously indicated, the invention is dis closed herein as embodied in an apparatus for automatically steering a pilotless glider to a source of radiation which differs in intensity or other characteristic from that of the field or objects surrounding it.

The apparatus may include, and is disclosed herein as including selectively operable controls whereby the glider (or other vehicle) will follow a chaser course or a navigational course.

By chaser course is meant a course of travel wherein the target seeking vehicle is made to point and travel toward the target at every instant during its travel, within the limits of accuracy of the apparatus. With changes in direction of travel made at finite intervals and at finite rates, a chaser course does not result in the vehicle meeting the target with geometrical accuracy, but under many conditions a vehicle traveling on a chaser course toward a moving target will strike the target, especially if the latter is of reasonable size.

By a navigational course is meant a course of the vehicle which is, in effect, the result of computation based upon previous successive observations of the position of the target relative to the vehicle. By this method the vehicle is steered not directly toward the target, but instead is steered toward a point at which the target will be when the vehicle reaches the same point. In utilizing the navigational course method of steering the vehicle, the apparatus must repeatedly make observations of the position of the target and repeatedly modify its prediction of the location of the point at which the vehicle will strike the target, and must operate the steering controls of the vehicle accordingly.

In using the apparatus on a vehicle maneuverable in three dimensions, such as an airplane or glider, the observations, the steering, and the predictions, must of course be made not only with reference to the azimuthal directions, but also with reference to directions in a vertical plane.

The apparatus herein disclosed may be conditioned to operate on the chaser course 'or the navigational course principle in both azimuth and vertical plane, or it may be conditioned either to travel a chaser course in azimuth and a navigational course in the vertical plane or vice versa, depending upon the circumstances under which the apparatus is to be used.

The means for detection of the target comprises two pairs of radiation responsive devices shown as phototubes which, through an oscillating telescopic head, receive light from the field scanned. One pair of tubes receives light from adjacent rectangular areas, which rectangular areas, due to the oscillation of the head, laterally traverse a rectangular field, while the other pair of phototubes receives light from similar adjacent rectangular areas which traverse a rectangular field below that of the first rectangular field and preferably over-lapping it slightly.

The phototubes supply signals to an amplifying system. The amplifying system constitutes two cascaded amplifiers, one for each pair of phototubes. The amplifiers include novel automatic volume controls, each such control being common to corresponding stages of the two amplifiers, the arrangement being such that upon starting the apparatus all stages provide maximum gain, but that as the signals from the photo of radiation from portions of the field other than the target, and which are of no significance, are not transmitted through the amplifiers.

The output signals of the amplifiers are switched in synchronism with the scanning oscillation of the head to four control circuits so that these circuits may provide, by their energization, an indication of the location of the target in the over-all field of view being scanned. For purposes of description hereinafter, the four quadrants of the generally rectangular field scanned by the apparatus will be designated; UR, upper right or first quadrant; UL, upper left, or second quadrant; DR, lower (down) right or fourth quadrant; and DL, lower (down) left or third quadrant. In specifying a direction, the usual mathematical vector convention may be employed, i. e. positive is counter-clockwise, or toward the left, and negative is clockwise, or toward the right.

Thus, significant signals from the amplifiers energize one or more of these control circuits which, through relays, control the operation or means for steering the glider. As shown herein, these means comprise motors operating upon the manual control button shafts of a well known automatic gyro-pilot.

Selective means are provided to determine whether a significant signal from the amplifier during R--L, or LR, or both R -L and L--R strokes of the oscillatory head shall be efiective to energize the control circuits. When the apparatus is set for a chaser course the control circuits are arranged to cause steering of the glider toward the target, that is, the glider is maintained pointed at the target, or is kept pointed a predetermined angle oiT the target to allow for windage. Assuming that the speed of the glider is very high with respect to the speed of the target, the glider will eventually strike the target. In the case of a glider to be used against vessels at sea, the glider will preferably be provided with a hydrostatic pressure-controlled detonator so that the explosion will not take place until after the glider has struck the side of the vessel and dropped into the Water adjacent thereto, thus securing maximum efiectiveness of the explosive against the hull of the vessel.

Various manual control circuits are provided for initially testing the apparatus as a whole, for aiding in picking out the target, and for predetermining the character of the operation of the apparatus.

The scanning head The scanning head, as shown in Figs. 3 to 6,

is mounted on a base I00 which is adapted to be rigidly secured to the glider or other vehicle. A

U -shaped frame, comprising joined vertical channels I62, I 04 and a horizontal channel I06, is mounted for limited rotational movement about a, central pivot I08, the frame having a plurality of pedestal brackets IIO secured to the channel I06, these brackets having foot portions I I2 resting upon the upper surface of the base I09.

A rectangular gimbal II 4 has pivot studs II6 projecting horizontally into suitable bearings fixed near the upper ends of the channels I 92 and I04. A pair of telescope tubes H8 and H9 are secured to each other by plates I20, I2I which may be welded or otherwise secured to the tubes I I8, I I 9. A central pivot shaft I24 is rigidly secured to the plates I20, I2 I, and is mounted in bearing bushings I25 and I21 fixed in the gimbal N4, the arrangement being such that the telescope tubes H8 and H3 are supported by the shaft I24, and thus may oscillate with respect to the gimbal I I4.

Optical system Each of the tubes I I6, I I9 contains a condensing lens system illustrated as comprising a pair of lenses I26. A light shade I28 is secured over the ends of the tubes H8, H9 and contains a plurality of peripherally flanged baffie supports I30 having progressively decreasing circular openings therein, the flanges of these baiile supports forming accurate positioning spacers.

Light bafiles I32, which may be of thin dull black paper or other similar suitable material, are cemented to the bafiie supports I30 and have circular openings of progressively decreasing diameter formed therein, these openings being co-axial with the optical axes of the lens systems, and each of slightly less diameter than the openings in the supports to which they are attached. The baflle supports I30 are finished in dull black so as to minimize the possibility of a reflection of light therefrom into the lens system.

A light slit member I34 is secured within each of the tubes I I8, I I9 at a point adjacent the focus of the lens system, this member having an elongated vertical slit I36 formed therein. Directly behind the slit I36 of each of the telescopes is a reflecting prism I38, extending at least the full length of the slit, and mounted on vertical pivots I39. Each of the pivots I39 extends through the top of the telescope tube and has an arm I40 rigidly secured thereto. The arm I40 is held against the end of an adjusting screw I42 by a strong tension spring I44. It will be apparent that byturning the adjusting screw I42 the prism I38 may be rotated about the axis of its pivots I39 so as to have its edge accurately centered behind the slit I36.

The prisms I38 are preferably made of metal, such as steel, plated with a metal providing good reflecting surface, such as chromium.

Light reflected from the surfaces of the prism I38 in the tube H9 enters phototubes I46, I41, while light entering the telescope tube H8 is reflected by its prism to phototubes I48 and I49 61 (Fig. 1a). A shielding box I50 is mounted within each of the tubes H8, H9 and contains a preamplifier later to be described.

Telescope oscillating mechanism As best shown in bottom plan section in Fig. 6, a pair of solenoid coils I52, I53 are rigidly secured to the gimbal II4 by being clamped in a pair of bolted bracket members I54 which are rigidly secured to the gimbal II4. A bracket I56 is also rigidly secured to the gimbal I I4 and has a downwardly extending lug I59 to which one end of the heavy leaf spring I60 is riveted. The outer end of the leaf spring I60 is secured to the end of a second relatively short leaf spring I62 by means of an angle I64 riveted to the springs. The other end of the leaf spring I62 is secured to a bracket I66 which is riveted to the plate I20.

The leaf spring I60 .is best shown in Fig. 6 in its normal unstressed position, and will thus be capable of applying a force tending to return the telescope tubes to this center position whenever the tubes are displaced from this position. The oscillation is effected by alternate energization of the coils I52, I53 which operate on solenoid plungers I68 and I69 respectively, these plungers being partly of magnetic and partly non-magnetic material and each having one end pivotally secured respectively to studs I10 riveted to the plate I20. The other ends of the plungers I66, I69 are pivotally secured to the ends of a lever I12 which is mounted for pivotal movement about a central pivot I14 carried by the imbal I I4.

The plungers I68, I69 and the lever I12 and plate I20 thus form a parallelogram linkage with the result that the plungers I68 will retain parallelism throughout their movement. In order to oscillate the telescopes H8, H9 the coils I52, I53 are alternately energized by means hereinafter to be described. These solenoids operate against the resiliencyof the spring I60, and as will hereinafter appear, are energized alternately, each throughout substantially the complete stroke of the telescope tubes in one direction, and the spring I60 supplies the force to cause commencement of the stroke in the opposite direction.

A stud I16 is riveted to the plate I2I and thus oscillates with the telescope tubes. The upper end of this stud I16 has flats formed thereon and projects through an arcuate slot I18 formed in the end of an arm I80. The effective ends of the slot I18 are determined by adjustable buffers I82 of felt, or similar material, which are secured in adjusted position by bolts I84. The arm I90 is pivotally mounted on the bushing I25 (Fig. 7) and rests upon a shoulder I66 formed on this bushing. A relatively stiff spring washer I88 presses the arm I against the shoulder I86, the degree of pressure being determined by adjustment of a nut I90 held in adjusted position by a lock nut I92. Thus, as the oscillating head approaches the ends of its oscillatory stroke, the stud I16 abuts against one of the stops I82 and the motion of the head is quickly retarded to a stop by virtue of the friction between the arm I80 and the shoulder I86.

It will be noted (Fig. 5) that the telescope tube II9 is not exactly parallel to the tube H8. The optical axis of the tube H9 is elevated with respect to the optical axis of the tube H8. This elevation, in the embodiment illustrated, is 4. As a result, the phototubes are capable .of scanning a field diagrammatically :shown in Fig. 8.1.

Referring to this figure, when the oscillating head is in central position, the phototube I46 will receive light from the area I46a, and the phototubes I47, I48 and I49 will receive light from the areas designated respectively I4'Ia, I48a and I49a. The angular dimensions of each of these areas are 4 /2" in the vertical direction and in the horizontal direction. The head oscillates through a total angle of 18 represented by the dotted line rectangle in Fig. 8, but because of mechanism later to be described, the signals from the phototubes received during the first 1 of each oscillation are not effectively utilized, and the total field effectively scanned is therefore represented by the large full line rectangle I94 which has angular dimensions of 8 /2 by 15. It will be noted that the areas M611 and Mia respectively over-lap the areas M811 and I490. by /2. The rotary moment of inertia of the telescope tube assembly is of such value relative to the resiliency of the spring I60 and the pull of the solenoids, and relative to the friction applied by the arm I30, that the oscillation of this assembly is smooth and at a uniform speed, in the order of 2 cycles per second.

Stops, such as rubber covered pins I93, I95 (Figs. 3 and 5) adapted to engage the gimbal I I4, may be provided to limit the extent of oscillatory movement of the telescope tubes.

Head indexing mechanism In some uses of the apparatus, it is desirable to provide means for changing the elevation of the scanning head relative to the base I00, either as an initial adjustment, or as steps in following a navigational course. This is accomplished by means of a reversible electric motor I96 suitably secured in the vertical channel I04 and including a reduction gearing terminating in a pinion I98. This pinion meshes with a gear segment 200 rigidly secured to the gimbal pivot pin H6. The driving action of the pinion is limited by recesses 20I formed in the segment 200. The motor I90 may be manually or automatically controlled, as will hereinafter appear, and thus will operate to swing the gimbal I I4 and all parts carried thereby for the purpose of changing the elevation of the telescope tubes I I8, II9.

In some uses of the apparatus it may be convenient to have available remotely controlled means to adjust the orientation of the frame with respect to the base I00, and hence with respect to the vehicle upon which the apparatus is mounted. Such adjustment is essential when the apparatus is used to cause the vehicle to follow a navigational course as herein described. For this purpose a motor controlled means is provided to rotate the frame I02, I04 and I06 about the pivot pin I08. This means comprises a motor and reducing gear train 202 having a slow speed drive shaft 204. A bevel pinion 206, secured to the shaft 204, drives a bevel gear 208 secured to a shaft 2 I 0. The shaft 2 I 0 is mounted in a suitable bearing bushing 2I2 secured in the channel I06, and has a pinion 2I4 secured to its lower end. The pinion 2I4 meshes with a ring gear 2I6 secured to the base I00.

An arcuate contact segment 2I8 is mounted in the base I00 and insulated therefrom. A switch arm 220 secured to the horizontal frame channel I06, but insulated therefrom, is capable of wiping over the contact segment 2 I0 and make contact therewith when the frame is shifted from its normal central position to the right with respect to the base I00. The motor 202 is a reversible motor and is controlled by means hereinafter to be described.

Head operated switches Switches I and S respectively comprise switch arms 222, 223 (Fig. 6) which are frictionally secured to the gimbal I I4 but insulated therefrom. The switch arm 222 carries a contact element 224 which moves relatively between contacts 226 and 228 which are secured to but insulated from the plate I20. Similarly, the switch arm 223 has a contact 225 which may move relatively between a pair of contacts 221 and 229, the contacts 221 and 229 being mechanically secured to but insulated from the plate I20.

Each of the contacts 226 to 229 has one end of a thin flexible resilient metal band 230 connected thereto, the other ends of these bands being anchored in an insulating terminal block 232 which is suitably secured to the gimbal II4. It will be noted that the flexible bands 230 are formed symmetrically in bights so that the resilient forces exerted thereby between the oscillating telescopes and the gimbal II4 are balanced. The bands are spaced sufficiently in a vertical plane so as not to make contact with one another. At their ends adjacent the terminal block 232 the bands 230 are formed with soldering lugs for attachment with suitable conductors, which are combined to form a flexible cable 233. The switch arms 222, 223 are likewise connected by bands 230 leading to the terminal block 232. In general, the mounting of the switch arms 222, 223 may be similar to that shown in the patent to David Hancock, Jr. No. 2,301,870.

It will be seen that as the telescope tubes IB, I9 swing in one direction relative to the gimbal I E4, contact 223 will engage contact 224, and contact 229 will engage contact 225. At the beginning of the reverse stroke of the telescope tubes, the aforementioned contacts will be broken, and shortly thereafter (about 1 of movement) the contact 226 will engage contact 224, and contact 221 will engage contact 226. These contacts will remain closed throughout the return stroke and will be broken only upon the commencement of another forward stroke.

A switch A comprises an arm 234 (Figs. 3 and 4) which is secured to the gimbal I I4 but suitably insulated therefrom, and has a contact point engageable with a conducting plate 236 embedded flush in an insulating block 238 which is rigidly secured to the frame channel I04. Thus, when the telescope tubes are elevated slightly above their normal positions (swung clockwise, Fig. 4), the switch arm 234 will make contact with the plate 236, and this contact will be broken whenever the telescope tubes are depressed (swung counterclockwise, Fig. 4) slightly below their normal horizontal position.

A switch D comprises flexible switch arm 240 which has one end suitably secured to an insulating terminal block 242 attached to the top of the gimbal II4. Also secured to this terminal block is a switch contact 244 adapted to be engaged b the switch arm 240.

A switch contact member 246 is rigidly secured to the plate I2I but insulated therefrom and is adapted to engage the free end of the switch arm 240. Suitable contact points are secured to the switch arm 240 or to the switch parts 244 and 246, or both.

As the telescopes oscillate in a counterclockwise direction from their central position shown ly therewith) breaking the contact between the switch arm 240 and the switch contact 244.

Upon return of the telescopes to their central position, the switch arm 240 again makes contact with the switch contact 244, while immediately thereafter (substantially instantaneously therewith) the contact between switch member 246 and the switch arm- 24!) is broken, since further fiexure of the switch arm 240 is prevented by its engagement with the rigidly mounted switch contact 244. This switch mechanism including the parts 240 to 246 is designated generally by" the letter D. A switch U (Fig. 3), of construction identical with that of switch D, is mounted on the gimbal I I4 directly beneath switch D, and operates in the same manner as switch D.

A switch K (Fig. 5) constructed and operating exactly like switches D and U is mounted on the gimbal II4 above the telescope tube I I9.

As best shown in Figs. 3 and 9, there is suitably secured to each of the telescope tubes II 8, I I9, an insulating block 250, and there is secured to the gimbal H4 3, long insulating block 252. A plurality of thin resilient strips 254 of Phosphor bronze or similar material are formed in semicircular bights of successively smaller radius, and each of these strips has one end anchored to one of the insulating blocks 250 and its other end anchored to the insulating block 252. The ends of these strips 254 project through the insulating blocks and form soldering lugs for attachment of wires leading from the phototubes and preamplifier to the amplifier.

It will be noted that as the telescope tubes oscillate (approximately 9 to the right and 9 to the left of the central position shown), the strips 254 will flex, but substantially maintain their relative separation. One group of strips opposes the other group of strips so that they exert the least force when the telescope tubes are in central position, and the resiliency of these strips thus supplements the resiliency of the spring I60. Since these strips 254 may flex freely and are not in 'contact with one another, and since they are firmly anchored at their ends, they do not introduce any appreciable frictional forces nor absorb power from the telescope oscillating motor means. This type of flexible connection istherefore far superior to any flexible pigtail or cable through which the circuits to the phototubes and preamplifier might otherwise be completed.

The amplifying system By reference to Fig. 2, the relationship of Figs. la, 12), 1c, 1d and 1e will be apparent. The circuits of Fig. 1b are connected to the circuits of I I Fig. 1a by conductors II] to I1 inclusive, while the circuits of Fig. 1d are connected to the circuits of Fi 1a bv conductors 20 to 31 inclusive. The circuits of Fig. 1e are connected to the circuits of Fig. 1:1 by conductors 25 to 29 inclusive and 38 to 66 inclusive.

The amplifying system (except for the first stage of preamplification) is shown in Figs. 1b and 1c, and the apparatus shown in these two figures is preferably contained in a separate shielded. box. Similarly, all of the parts shown in Fig. 1d may be mounted in a separate box, while the parts shown in Fig. 1e may be contained in part in a box attached to the gyro-pilot control panel, and in part in a separate control switch box.

Referring to Figs. 1a and 1b, the conductor I0 is connected to a v. terminal of a battery 256 through a filter resistor R251. The conductor Ill is shunted to ground through a condenser C255 and thus supplied a 90 volt potential to the anodes of phototubes I46 and I48. The cathode of phototube I 46 is connected by a conductor 258 to the anode of phototube I41, while the cathode of phototube I41 is connected to ground. Similarly, the cathode of phototube I48 is connected by a conductor 259 to the anode of phototube I49, while the cathode of the latter is connected to ground.

The conductor 258 is connected through a condenser C260 and spurious high frequency filtering series grid resistor R262 to the grid 264 The condenser of a preamplifier pentode 266. C260 is also connected through a grid resistor R268 to ground. In a similar manner a condenser C26I is coupled to the grid 265 of a pentode preamplifier tube 261. The screen and suppressor grids of the tubes 266 and 261 are connected with their plates 210 and 21I respectively to conductors II and I5 respectively, so that these tubes will operate as triodes and provide class A amplification. The cathodes 212 and 213 of these tubes are connected respectively to conductors I3 and I4. Conductor I3 is connected to ground through a self bias resistor R214 and a jack switch 216, while the conductor I4 is similarly connected to ground through resistor R215 and a jack switch 211. Upon insertion of plugs in these jacks, these switches 216 and 211 are opened.

The jacks 218 and 219 are provided for plu ging in a milliammeter for adjustment and checking purposes. For example, in order properly to adjust the reflecting prisms I36, I39, using such milliammeter, the adjusting procedure would be as follows: The optical system would be pointed toward a field of uniform illumination and the sight openings of the telescope tubes completely obscured by a black sheet. The meter reading would then be noted and the sheet'would then be quickly raised vertically and the motor reading again noted. If during the time that the sheet is being raised. the meter needle fluctuates in either direction, it indicates that the prism is not properly centered and correcting adjustment may then be made. A meterinserted in 'these jacks may also be used for testing purposes to indicate that the proper plate current is flowing in the tubes 266, 261.

In general, as the telescope and phototubes oscillate and view an object radiating more light than the surrounding uniform field, the phototube I 46 will first supply a positive signal to the grid 264, and immediately thereafter as the tube I41- receives light from such object, the grid 264 will receive a negative impulse. Upon the return oscillation of the scanning head, the phototube I41 will transmit a negative impulse to the grid 264, and immediately thereafter the phototube I46 will provide a positive impulse on the grid 264. The impulses supplied to the grid under these assumed ideal conditions are represented by the wave shown in' Fig. 10. The output of the first preamplifier tube would be a similar amplified wave of opposite phase.

Plate current for the preamplifier tube 266 is provided through a resistor R282 connected between the +90 v. terminal and the conductor I I,

and in a similar manner plate current is supplied for the tube 261 through a resistor R283. The preamplifier tube 266 is coupled to a second stage of preamplification, comprising a pentode 284, through a blocking condenser C286, a high pass filtering mesh comprising condensers C290 and C294, and resistors R288, R292 and R300, and through a spurious high frequency filtering series grid resistor R296.

The grid 298 of the tube 284 is biased through the grid resistor R300 which is connected to a terminal -l.5 v. of a biasing battery 332, the positive terminal of which is connected to ground. The cathode 334 of the pentode 284 is connected to ground, while its screen and suppressor grids are connected to its plate 306, plate current being supplied from a +90 v. terminal through a load resistor R308. The pentode 284 thus operates as a triode providing class A amplification.

The output of the pentode 284 is coupled to the input circuit of a signal amplitude limiting pentode 310 through a blocking condenser C3I2, and a voltage divider comprising resistors R3l4 and EMS. The junction 3I8 of resistors R3l4 and R316 is connected through a series grid resistor R320 to the grid 322 of the pentode 3H]. The other terminal of the resistor R3l6 is connected to a 1.5 v. terminal.

The suppressor grid of the pentode 3! (which may be of the 6W7G type) is externally connected to the grounded cathode 324, while the screen grid 326 is connected to a +45 v. terminal of battery 256. Plate current is supplied through a load resistor R328 from a +90 v. terminal.

The pentode 3H3 operates in a manner to reduce the amplification of the low value positive peaks of the wave, and to increase amplification of the negative half of the wave as diagrammatically illustrated in Fig. 11. In this figure the curve Ha represents the grid voltage-plate current characteristic, for negative grid potentials,

of a 6W'7G pentode connected as is the tube 3H] shown in Fig. 11).

Two input waves I lb and He are indicated on the grid voltage axis lid. The resultant output 7 waves of the tube are illustrated as He and Hf respectively. From this diagram it will be noted that when the amplitude of the input wave, such as HZ) (representing the signal due to a distant target), is not very great, the tube operates substantially to cut oiT the positive peaks of the input wave to the grid and to amplify linearly the negative peaks. The positive portions of the output wave He are reduced in amplitude due to the effect of the series grid resistor RZQG When the grid potential is positive with respect to the cathode, the grid input impedance falls to a finite value, small relative to the value of R296, with the result that there is a voltage divider action, causing the signal on the grid to be greatly reduced. When the input wave on the grid is of much greater amplitude, such as shown by the wave Ilc (representing the signal due to a close target), the tube operates not only to cut ofif the positive portion of this input wave The particular purpose of this type of operation of the tube will appear from the description of the operation of the system as a whole.

The output of the pentode 3H3 is connected to the input of an automatic volume control triode 330 through a blocking condenser C332 which also forms part of a high pass filter mesh including resistors R334 and R336. A grid con denser C338 is connected between the junction of resistors R334, R338 and the grid 330. The rid 340 is connected to a 1.5 v. bias terminal through a resistor R332 of a value in the order of 3 megohms and a resistor R343 of high value in the order of 50 megohms.

When the signal to this grid is large, by comparison with the negative grid bias, grid rectification takes place with the resultant automatic biasing of this grid to a negative potential higher than the normal grid bias.

The grid condenser C333 may have a value in the order of .1 mid. with the result that it will take an appreciable time interval after a decidedly positive impulse upon the grid 340 before the grid returns to its normal value bias of 1.5 v.

Assuming that the head oscillates at 2 cps, the values of the condenser C338 and registers R342 and R344 are such that it will take more than .5 second (and in actual practice may be in the order of 5 to 10 seconds) for the grid to return to substantially its normal -.l.5 v. poten tial after a substantial amplitude positive signal has been impressed thereon. The result is that as a close succession of positive impulses is impressed upon the grid 336, appreciable changes in plate current will take place only upon the highest amplitude positive impulse.

The plate 346 of the triode 330 is supplied with plate current though a load resistor R348 connected to a v. terminal, and the signal co1nponent of the plate current is transmitted through a blocking condenser C350, through a voltage divider network comprising resistors R352 and R354, and a grid resistor R356 to the control grid 358 of a phase inverting triode 3-89. The cathode 332 of this tube is connected to ground through a biasing resistor R333.- Plate current for the triode 363 is supplied through a load resistor R366.

The tricdes 330 and. 350 and associated circuit elements comprise a single stage of amplifying and volume control. The output of the phase inverter triode 361] is transmitted through a band pass filter mesh 3'59 to the input of an automatic volume control triode 316, and the output of the latter is transmitted through a high pass filter and voltage dividing mesh 380 to a phase inverting triode 382.

The output of the triode 382 is coupled to the input of an automatic volume control triode 338 through a band pass filtering mesh 390. The output of the triode 336 is coupled with a voltage divider and high pass filtering mesh 392 to the input of a phase inverting triode 393.

The output of the phase inverting triode 356 is transmitted through a blocking condenser C398 to a conductor I6. Triodes 316 and 382, and the circuit elements associated therewith, are in substance identical with triodes 333 and 360 and the circuit elements associated therewith, and thus form a second cascaded stage of amplification and automatic volume control. Triodes 386 and 396 and the circuit elements associated therewith are likewise similar to the triodes 330 and 360 and their associated circuit 13 elements, and thus constitute the third and final cascaded stage of amplification and automatic volume control.

The output of the preamplifier tube 28'! (Fig. 1a) is coupled through conductor l to the input of the second stage preamplifier pentode 285 which, with its associated circuit elements, corresponds to the pentcde 284 above described. Likewise, tube 3H corresponds to tube 310 and is coupled to tube 285 in the same manner that tube 3"] is coupled to tube 284. In a similar way, the triodes 33!, 36!, 312', 383, 381 and 391, together with their associated circuit elements, correspond respectively to triodes 330, 360, 316,

382, 386 and 396 and their associated elementsrespectively. The output of the triode 39'! is transmitted through a blocking condenser C399 to a conductor ll, the conductors l6 and I! being respectively connected to ground through resistors R400 and R40l.

While the above described amplifier elements having reference characters which are even numbers may be identical with the corresponding parts of the amplifier whose elements bear reference characters which are odd numbers, it will be noted that the bias voltage for tubes 330 and 33l is supplied through a common resistor R344 and individual relatively low value resistors R342 and R343 respectively. As a result, the grid bias on the triodes 338 and 33| will be substantially the same at all times. From this it will be apparent that as one of the amplifier triodes is made less sensitive by having impressed thereon a high amplitude signal, the sensitivity of the other triode is correspondingly reduced. In the same way automatic gain control triodes 316 and 31'! are supplied with biasing voltage through a common resistor R314 of high value (in the order of megohms) which has one terminal connected to a1.5 v. terminal, while the grids of triodes 316 and 311 are connected to the other terminal of the resistor R314 through relatively low value (in the order of 3 megohms) resistors R312 and R313. Thus, these corresponding stages of the two amplifiers are likewise retained at substantially equal sensitivity. Similarly, the grid bias for triodes 386 and 387 is supplied through a common resistor R384 which has one terminal connected to a -1.5 v. terminal, and has its other terminal connected to the grids of the tubes 386 and 38'! through relatively lower.value resistors R382 and R383 respectively, and these corresponding stages are likewise maintained at equal sensitivity.

Operation of the amplifying system Let us assume that the apparatus is scanning a field illustrated in Fig. 14 in which appears a boat T which is lighter than the background,

i. e., its radiation of light of a frequency to whichthe phototubes respond is more than that of the remainder of the field. At the initial great distance between the boat and the apparatus, large whitecaps and other discolorations of the water, small floating objects, etc., provide such minor variations in radiation that they are very small compared to the change in intensity of radiation as the phototubes M8, 147 scan the boat in the upper half portion of the field. The sig-- nal produced by the phototubes M8, I41 will therefore be somewhat similar to the wave shape illustrated in Fig. 12 as the head traverses a complete cycle. This signal from the phototubes I46, [4! will be faithfully transmitted through the preamplifier pentodes 266 and 284 and will be of the input signal.

impressed upon the grid of the limiter tube 3|!) which, due mainly to the series grid resistor R320 responds only to the relatively high amplitude negative peaks of the received signal and will thus have an output, as previously mentioned, similar to the wave of Fig. 13. Through means, hereinafter to be described, the apparatus will be steered toward the target so that at some time later the target may appear in the field of view of the apparatus as indicated in Fig. 15. At this close range the apparatus would also be sensitive to variations in radiation resulting from other objects such as whitecaps, clouds, etc., or other small floating objects indicated generally as F.

The amplifier, however, operates in such manner that signals from the phototubes, due to such objects as F, are ignored. This is accomplished because of the fact that the triode 386, due to the regular reception of high amplitude signals, is biased so far negatively that only the highest amplitude positive peak signal will be transmitted by this tube. Since the signal is amplified to the greatest extent in this last stage represented by the triode 386, this will be the first automatic volume control triode to be rendered insensitive to any' but the highest amplitude positive peaks As the apparatus approaches closely to the boat T, the amplitudes of the signals impressed upon the triode 316 will be such as to increase negatively the bias on this triode to make it transmit only the highest positive peak of its input signals. Similarly, as the apparatus arrives still closer to the boat T, the input signal on the triode 338 becomes of such high amplitude that this triode is also biased negatively to such an extent that it is, in effect, cut off except for the highest amplitude positive signal of its input. Thus, for example, as the apparatus approaches so closely that the boat T appears in the proportion indicated in Fig. 15 the signals from the phototubes, due to variations in intensity as a result of scanning the objects F,

' are not of sufiiciently high amplitude to be transmitted by either the triodes 386, 316 or 338, since the grids of these triodes are at plate current cutoff for signals of these amplitudes.

However, as the boat T appears larger in the field of view of the apparatus, as shown in Fig. 1'7, the differences in radiation from the various portions of the boat would, if means were not provided to prevent it, have a significant effect. For example, as the phototubes I46, I41 scan the superstructure (or cabin) Tc of the boat T they produce the maximum signal, whereas it is desired to control the direction of travel of the apparatus not to the point from which the radiation is greatest, but from a selected point such as the bow Tb of the boat. The amplifying system will transmit substantially equivalent signals as the phototubes I46, I41 scan the bow Tb, cabin To and stem Ts, as shown in Fig. 18. Other elements of the control apparatus, hereinafter to be described, are designed to accept for control purposes only the first of such series signals received during selected scanning strokes (i. e. LR or Rr-L, or both L-R and RL).

Because of the use of the limiter tube and the successive stages of automatic volume control whereby the sensitivity of the amplifier as a whole decreases successively as the amplitude of the maximum signal received increases, the amplifier utilized to provide indications of the positions of the bow Tb and the stern Ts. The vehicle steering apparatus, as will hereinafter appear, will tend always to point the apparatus in a direction such that the boat or other target will appear at the center of the field scanned.

The phototubes I48 and I49 scan the lower quadrants of the rectangular field of view of the apparatus in the same manner as the phototubes I46, I41 scan the upper quadrants, and the foregoing description of the operation of the amplifying system for the upper quadrants will apply equally to the amplifier for the signals from the lower quadrants.

Due to the common bias voltage supply for the corresponding automatic volume control triodes of the successive stages of the two amplifiers, the degree of sensitivity of the two amplifiers is kept approximately the same. Thus, it is the highest amplitude signal received from an object in any one of the four quadrants which will be transmitted by its associated amplifier, and

which will prevent either of the amplifiers from transmitting any signals of lesser intensity.

If, for example, the apparatus has its field of view violently shifted as by an air pocket or a gust of wind so that the boat T appears in the lower half of the field, the false target objects F will, nevertheless, not be capable of producing a significant output signal from the amplifiers because due to the common bias source for the corresponding automatic volume control triodes of the two amplifiers, the two amplifiers will at each instant be operating with the same gain, and be incapable of transmitting any but the highest amplitude signal. a

The foregoing description of the operation of the amplifier can be summarized in a general way as follows: When the apparatus is a great distance from the target and the signal is correspondingly very small, the entire operation of the amplifier is linear, therefore the highest signal produced will be the significant signal. As the apparatus approaches closer to the target the automatic volume control tubes start to function, and the highest signal is still the significant signal. When the apparatus has approached so closely to the target that all portions of the target cause the limiter tube to be completely overdriven, the significant signal now becomes the first one received during any cycle of scanning.

For reference purposes the amplifier as shown at the top of Figs. 1a, lb and 1c, and which responds to signals received from the upper half of the whole field scanned, will be referred to as the Up amplifier and as providing an Up signal. The amplifying system shown beneath the upper amplifier and which responds to signals from the phototubes I48, I49 will be referred to as the Down amplifier. When the target produces a signal in the Up amplifier it generally means that the direction of travel of the vehicle must change in an upward direction, while when the target appears in the lower half of the scanned field and produces a signal in the phototubes I48 and I49 and is transmitted through the Down amplifier, it usually means that the vehicle must change its course downwardly in order to keep directed toward the target.

The control circuits the conductor 20. In a similar way the grid 401;

of the tube 404 is connected through a protective resistor R409 and blocking condenser C4II to the conductor 2I. Conductors 20 and 2| are respectively connected to ground through shunt resistors R4I2 and R4l3, while the grids 406 and 401 are respectively connected to a -l.5 v. termi nal of a biasing battery H4 through grid resistors R4I6 and R ll'i.

The cathodes 4I8 of the four tubes 402 to 405 are connected to ground through a common bias resistor R420. Plate current for the operation of the tubes 402 to 445 is supplied through the conductor 24 (through a circuit hereinafter to be described), the conductor 24 being connected through ignition maintaining protective resistors R422 to the plates 423 respectively of each of these tubes. Plate current of tube 462 may also flow through a relay winding UR (UpRight) which is connected between the plate and the conductor 24. Similarly, a relay winding UL (Up-Left) is connected in the plate circuit of the tube 404. A relay winding DR (Down- Right) is connected in the plate circuit of tube 403, and a relay winding DL (DownLeft) is connected in the plate circuit of tube 405.

The relay UR when energized is adapted to .close switches URI, UB2 and UR3, and similarly,

relay UL when energized closes switches ULI, UL2 and UL3. The relay DR when energized closes switches DRI, DR2 and DB3, and relay DL when energized closes switches DLI, DL2 and DL3. A condenser C424 is connected between the conductor 24 and ground and reduces arcing at switch contacts associated with conductor 24, and stores energy to be supplied when plate current commences flowing in any one of these tubes.

Since the cathodes of the four triodes 402 to 405 are connected to ground through the common resistor R420, the ignition of any one of the tubes will swing the cathodes of the other tubes so far positive that any subsequent positive signals on their grids are ineffective to cause ignition. These gaseous triodes thus form a means to select for utilization, the first only of the signals which may be impressed on the grids of any one of these triodes.

The signals from the upper amplifier are transmitted through its output conductor I6 to the switch U and thence to the conductor 20 during the interval that the scanning head is swung from its central position to its rightmost position and during its return to its central position, while conductor I5 is connected to the conductor 2| as the head moves from central position to its leftmost position and as it returns to its central position. Thus, it will be seen that the output signals of the upper amplifier are impressed upon the grid of tube 402 while the UR quadrant is being scanned, and thus may energize relay UR. Similarly, signals resultant from scanning the UL quadrant will be transmitted to the grid of tube 494 and energize the relay UL; signals resultant from scanning the DR quadrant will be transmitted to the grid of triode 403 and may energize the DR relay; and signals resultant from scanning the DL quadrant are impressed upon the grid of triode 405 and may energize the DL relay.

The switches operated upon energization of the relay windings UR, UL, DR and DL determine the character of operation of the various steering controls, among these controls being those of the gyro-pilot shown in Fig. 16. In a well known form of gyro-pilot mechanism (such as the Sperry A-3 automatic gyro-pilot) the manual adjustment of the direction of flight is controlled by three manually rotatably knpbs including a knob, such as the knob 425 (Fig. 1e) which adjusts the control of the gyro-pilot upon the elevator. Turning the knob 425 to the right will depress the nose of the plane, while turning it to the left will elevate the nose of the plane relative to its previous position.

A similar knob 426 is used to adjust the control of the gyro-pilot upon the rudder. Rotating the knob 426 to the right will cause the plane to turn to the right, While turning this knob to the left will cause the plane to turn to the left. A third control knob 42'! is usually provided on the control panels of automatic gyro-pilots to adjust the effect of the gyro-pilot mechanism upon the ailerons. The control is such that when the knob 42'! is turned to the right the right aileron will be elevated and the left aileron depressed causing the plane to bank for a right turn, while when the knob 42'! is turned to the left the plane tends to bank for a left turn.

For the purposes of the pilotless glider (and possibly for other uses of the apparatus in steering aircraft) it has been found that it is not essential separately to control the ailerons, but that the ailerons may be adjusted as an incident to the movement of the rudder. It is therefore contemplated that the rudder and aileron controls will be interconnected in a suitable manner (depending upon the design of the airplane or glider on which the apparatus is installed), so that the airplane will bank suitably for the degree of turn which should result from movement of the rudder. Such interconnection between the rudder and aileron controls is indicated by a chain or belt 428 which passes around suitable sprockets or pulleys 429 and 436 secured to the shafts of the control knobs 426 and 421 respectively. In some cases the apparatus may be mounted on a glider not equipped with ailerons, since it has been found that a well designed glider can be made to fly in a stable manner when its azimuthal course is controlled solely by the rudder, provided that changes in the azimuthal course are not made too rapidly.

In lieu of the customary gyro-pilot control mechanism, a gyroscopic control apparatus of the type disclosed in my co-pending applications Serial Nos. 463,642 and 463,643, filed October 28,

1942, may be utilized. These applications have since matured into Patents Nos. 2,408,929 and 2,517,786 respectively.

In the present apparatus means are provided to adjust the position of the control knobs 425 and 426 automatically in order to steer the glider or airplane. These means comprise a'series motor 432 coupled to the shaft of control knob 426 by a suitable drive, diagrammatically indicated as a shaft 433, and a series motor 434 coupled to the shaft of control knob 425 in a suitable manner diagrammatically indicated as by a shaft 435. The motor 432 has a field winding 438, while the motor 434 has a field winding 440. Antispark resistors Rs are respectively connected in parallel with the windings 438 and 440 to reduce sparking at the switch contacts when the circuits including these windings are opened or closed. Throughout the apparatus such anti-spark resistors Rs are employed in parallel with inductive windings for the same purpose. All of such resistors, serving this purpose of reducing the sparking, are therefore designated by the same reference character, Rs. These resistors are of appropriate values, depending upon the inductance of the windings with which they are associated, from 10 to 150 ohms.

The horizontal index motor 202- (previously described with reference to Fig. 5) is shown in Fig. 1a as having a series field winding 442, while the previously described motor I96, for effecting vertical indexing of the telescope head, is illustrated in Fig. 1a as having a series field winding 444. Y I

Associated with the gyro-pilot control panel are four signal lamps designated 446, 441, 448

and 446 which, as will hereinafter appear, areilluminated whenever the relays UR, UL, DR and DL respectively are energized.

A plurality of relays are provided (Fig. 1d) to control the various motors and effect other switching purposeszRelays L (Left) and R (Right) which are respectively energized when the target appears in either of the left hand or either of the right hand quadrants; relays U (Up) and D (Down) which are respectively energized when the target appears in either of the upper or either of the lower quadrants; relay ID (Index Down) which, when energized, causes the vertical index motor to index the head downwardly; relay IU (Index Up) which, when energized, causes the vertical index motor I96 to index the head upwardly; relay IL (Index Left) which, when energized, causes the horizontal index motor 202 to index the head to the left; and relay IR (Index Right) which, when energized, causes the index motor 262 to index the head to the right.

All of the relays shown in Fig. 1d are arranged to have their movable switch elements swung upwardly when energized. Thus, when a relay L is energized it closes associated switches LI, L2 and L4 and opens switches L3 and L5; relay R, when energized, closes switches RI, R2 and R4 and opens switches R3 and R5; relay U, when energized, closes switches Ui, U2 and U4 and opens switches U3 and U5; relay D, when energized closes switches DI, D2 and D4 and opens ID3; relay IU, when energized, closes switch IU2 and opens switch IU3; relay IL, when energized, closes switch 1L2 and opens switches ILI and IL3; and relay IR, when energized, closes switch IR2 and opens switch IRS.

Whenever it is desired to render the apparatus operative to control the azimuthal course only of the vehicle, a rudder switch 450 (Fig. 16) is closed, and when it is desired to have the apparatus control only the vertical direction of travel of the vehicle an elevator switch 45| is closed. In normal operation of the apparatus both switches 45%! and 45! will be closed and remain closed and thus connect a +6 v. terminal respectively to the conductors 33 and 39. In fact, when the aparatus is installed on a pilotles glider, these switches may be omitted and the conductor 38 and 39 combined in a single conducto permanently connected to a +6 v. terminal.

.For testing purposes it is sometimes desirable to be able to control the relays R, L, U and D manually, and for this purpose switches 452, 453, 454 and 455 (Fig. 1e) are provided to connect conductors 44, 56, 5'! and 54 respectively to a +6 v. terminal. In normal operation of the apparatus, the switches 452 to 455 are open. In an installation of the apparatus on a pilotless glider, these switches may likewise be omitted.

Under some circumstances, it i desirable to 

